Known technology for hoisting or lifting systems on vessels, for example, drilling vessels, intervention vessels and service vessels used in the offshore market today, include winch-based systems (for example, so-called drawworks) with a multiple stringed block. These may be arranged in a single wire or in a multi-wire setup. An alternative solution is a cylinder lifting rig, such as the RamRig™ technology.
A conventional configuration with drawworks uses a drum which winds up a single hoisting wire with very high line speed, due to the gearing factor in the travelling- and crown block system. An example of a possible arrangement is described in NO 335499 B1. WO 2014/209131 A1 describes a further example of a winch-based hoisting system comprising a winch with a winch drum, an elongated hoisting member, and where the elongated hoisting member is accommodated in a single layer on the winch drum.
A cylinder lifting configuration may utilize cylinders pushing directly onto a yoke, on which a number of sheaves are attached. The hoisting wire is attached to an anchor at one end and to a load at the other end. The lifting speed is 2:1 between the load and the cylinder movement. A set of parallel wires can be arranged to lift a common load. An example of a possible arrangement is described in NO 301384 B1.
To comply with strict safety requirements, the hoisting wire in conventional drawworks systems needs frequent replacement, which is known as cut and slip operations. This is typically based on the number of lifting cycles and/or load cycles the wire is exposed to. Such replacement of lifting wire requires the hoisting system operations (for example, drilling) to be paused, thus resulting in downtime and increased costs and delays.
A further disadvantage is that energy is wasted for overcoming the moment of inertia and friction in the complete drum, gear and motors, as well as in wires and sheaves. This is particularly the case when operating at lower loads, as is normally the case for a large proportion of the operating time, and for systems with heave compensation capability, in which case the hoisting system will operate continuously to counteract the influence of wave loads on the vessel. Such operation requires significant energy and produces a large number of duty cycles on the hoisting system, requiring more frequent servicing (i.e., cut-and-slip operations).